A process of forming a silicon-based insulating film such as a silicon oxide (SiO2) film or a silicon nitride (Si3N4) film, in other words, an insulating film containing silicon as a predetermined element, on a substrate such as a silicon wafer or the like may be performed during manufacturing semiconductor devices. Silicon oxide films are widely used as an insulating film or an inter-layer film because of its high insulating property and low dielectric property. Silicon nitride films are also widely used as an insulating film, a mask film, a charge storing film, or a stress control film because of its high insulating property, high corrosion resistance, low dielectric property, and high film stress controllability. For the purpose of improving etching resistance, it is known to form a silicon oxycarbide (SiOC) film, a silicon carbonitride (SiCN) film, or a silicon oxycarbonitride (SiOCN) film by adding carbon (C) in the above silicon oxide film or silicon nitride film.
However, such addition of carbon into the insulating film may result in an increase in its dielectric constant and deterioration of its leak resistance while increasing its etching resistance. Thus, there are trade-off relationships between a low dielectric constant, a high etching resistance, and a high leak resistance. Although requirements for the above properties depend on use of the insulating films, there is a need to form an insulating film satisfying the requirements by increasing controllability of compositions in the insulating film.